NEW YORK, March 7 (Reuters) - A new fundraising group allied with President Barack Obama announced on Thursday that it will not accept corporate donations and will release the names of donors who give more than $250.

The announcement by Organizing for Action, a nonprofit group formed by former Obama advisers, comes amid criticism from Republicans, government watchdog groups and others that the group could be used not just to advocate for Obama’s agenda, but also to sell access to the Democratic president.

Because it is organized under U.S. law as a nonprofit, OFA, as it is known, may raise unlimited funds from individuals and corporations without disclosing its donors - as long as its advocacy focuses on issues rather than promoting candidates.

Similar groups poured tens of millions of dollars into the 2012 election campaign, much of it to support conservative and Republican candidates. Obama criticized the efforts, particularly the anonymity of donors to such groups.

Now, however, Obama’s allies are using the same formula to fund campaigns pressing for gun control and increased taxes on the wealthy, key parts of the president’s agenda.

Organizing for Action is planning an event next week in Washington for donors who have given more than $50,000. Those who give at least $500,000 can get a seat on the group’s advisory board and access to Obama and other administration officials, according to the Los Angeles Times.

That arrangement has drawn blistering criticism from some in Washington.

“Judging by recent reports, Organizing for Action should be renamed Paying for Access,” The Washington Post editorial page said on Sunday.

Jim Messina, Obama’s former campaign manager and the national chairman of OFA, said on Thursday that every three months the group will release the names of all its donors who give more than $250, along with how much they donated.

The group, Messina said, also will prohibit donations from corporations, federal lobbyists and foreign donors. A spokeswoman for OFA said the group will accept contributions from unions, a big supporter of Obama’s Democrats.

“We believe in being open and transparent,” Messina wrote in an opinion piece published by CNN.com.

‘VOLUNTARY DISCLOSURE IS VOLUNTARY’

Messina’s statement was the first time that OFA had detailed the level of transparency the group will provide about its funding.

The move may not satisfy campaign finance reform advocates.

“Voluntary disclosure is voluntary,” said Bill Allison, editorial director of the Sunlight Foundation, a nonpartisan group that seeks more transparency in campaign finance. “There is no way to check whether this is where they are actually getting the money or not.”

Republican strategist Karl Rove’s group, American Crossroads, which spent more than $100 million during the 2012 campaign, released an online video this week mocking OFA, saying it had put the White House up for sale.

“There has been some confusion about what Organizing for Action is and is not,” Messina wrote in his op-ed. “Organizing for Action is an issue advocacy group, not an electoral one.”

Messina said that the group’s ads would disappear from the airwaves in the months before the next congressional elections in November 2014.

“We will not advertise inside the campaign window,” a period defined by election law as 60 days before a general election, Messina said in an interview with Reuters on Wednesday.

“We are not a political organization, so the midterms don’t matter to us,” Messina said.

Obama supporters and campaign finance watchers predict that Organizing for Action has the potential to reach a broad audience, but Messina said that the scope and ambition of the group is still unknown even to its organizers.

One donor, a former Obama fundraiser, said the group wants to raise “tens of millions of dollars,” an amount that could make it a significant player in American politics - and a counter to conservative nonprofits.

Messina declined to provide a specific fundraising goal for his group.

“We’re figuring it out right now,” he said as he stepped outside of an OFA board meeting late Wednesday. (Editing by David Lindsey and Vicki Allen)